The present invention relates generally to the navigation of all manner of small boats, vessels and aircraft, herein called craft. As a boat is propelled and steered through the water, it moves with respect to the water. At the same time, the water may be moving with respect to the bottom and the shore as a result of a current. Likewise, an aircraft moves through the air which in turn may be moving with respect to the ground. The resultant motion of the craft is the net effect of these two motions combined, with regard to both direction and speed. The actual path over the bottom will not be the same as the heading steered, neither in terms of direction nor speed.
Persons conversant with the art to which the invention pertains are aware that navigation of such craft must take into account the offsetting influences that cause the actual path of the craft to diverge from the path steered. The offsetting influences for boats include tidal currents, oceanic currents and river currents. For aircraft, the offsetting influences include air currents and winds. For boats it is customary to use the direction into which the current is going; a Southerly current for example is flowing toward the South. For aircraft it is customary to use the direction from which the current is coming; a Northerly wind for example is coming from the North, but is flowing toward the South. These accepted usages must be considered in the design of navigational tools.
The influence of currents in the water or air, herein called the medium, can be a major factor in the navigation of these craft. The extent of the effect of these offsetting influences will vary widely with the relative speed of the current to the speed of the craft through the medium. For both types of craft, the navigational problem is the same. The navigator must obtain a correction to the heading of the craft relative to North and a true speed over the ground to offset the diverging influence of currents to properly navigate the craft from one point on the Earth to another. These navigational corrections can be determined from the speed of the craft through the medium, the strength of the current or speed at which the medium is moving relative to the ground, and the angle between the desired direction of travel and the direction of movement of the medium. The desired correction to the heading and a speed correction factor for true speed can be determined from this known information by a unique instrument incorporated in the present invention.
Prior art methods of finding a heading correction and computation of true speed, for navigating a craft to offset the influence of tide or wind, include tables, formulas solved by calculations, drawing vector diagrams, various types of multi-piece sliding calculators, and electronic calculators. Prior art has the shortcomings of being time consuming, or require involved computational skills, or require the use of complex equipment, or require external power sources in order to obtain heading and speed corrections. Further, the methods, tables and equipment for obtaining such corrections by prior art are expensive or difficult to replace and easily damaged or destroyed by the nature of the adverse environment sometimes found on small boats, vessels and aircraft. Because of the time required, or the difficulty of use, or the delicacy of the tools needed, obtaining heading and speed corrections by prior art methods is not always carried out under adverse conditions where such corrections are most needed. Further prior art often has the disadvantage of being set up for one system of units for speed and thus are of little use if a different set of units are selected by the navigator.
Accordingly, it is an objective of the present invention to provide an instrument that is quicker and easier to use than prior art for finding a correction to the heading and for determining the true speed of a craft to offset the influences caused by the motion of the medium through which the craft is moving. Another objective of the invention is to provide a rugged instrument of one piece construction with no moving parts that will not be easily damaged by the adverse conditions under which it may be used. Another objective of the invention is to provide an instrument that can be used for any set or range of units for speed. Another objective of the invention is to provide an instrument that is small, inexpensive and well suited for use on small craft where space and cost are important considerations. Another objective of the invention is to provide an inexpensive instrument that may also be used as a standard drawing triangle or straight edge by the navigator in the performance of his other duties.
The foregoing and other objectives of the present invention are obtained by constructing a unique and novel inscription of lines, circles and circular arcs on a thin sheet of transparent material, such as plastic, acrylic or other material having properties suitable for the objectives of the invention.
The principles used to construct the invention are now discussed. Geometrically, the craft speed through the medium may be equated to one unit of length on any convenient linear scale. The ratio of the speed of the tide or wind to the craft speed will then correspond to a segment of length of this unit scale. The angle between the direction of movement of the tide or wind and the intended direction of the craft will provide an angle. The unit length and the segment length and the angle constitutes two known sides and an angle of a triangle. From elementary trigonometry, the law of cosines and the law of sines may be used to find the remaining side and two angles of the triangle. By this mathematical principle, operation of the invention gives the heading correction angle and the speed correction factor for a craft to offset the effects caused by the motion of a tide or wind. On a logarithmic scale the product of two numbers is represented as the sum of two segments of the logarithmic scale. The ratio of two numbers is represented as the difference of two segments of the logarithmic scale. By this mathematical principle, operation of the invention gives the ratio of tide or wind speed to craft speed and the product of the speed correction factor times the craft speed .